The dermatology specialist nurse may perform the blood test, and they will usually take a sample from the arm, either inside the elbow or near the wrist, where the veins are near to the surface. In small children, samples may be taken from the back of the hand instead.

A tight band, known as a tourniquet, is tied around the arm, which causes slight swelling by temporarily slowing down the blood flow in the area, and makes it easier to obtain the blood sample.

Next, the area will be cleaned with an antiseptic wipe, to reduce the risk of infection.

A needle attached to a syringe is inserted into the vein, in order to draw the blood sample, and most people experience this as a slight pricking sensation, or a sharp scratch – but generally, a blood test is not painful.

Once the sample has been obtained, the tourniquet will be released and the needle removed. Pressure will be applied to the skin with a cotton wool pad, as this will help to stem the bleeding, and then a plaster will be applied to keep the tiny wound clean.

Usually the patient can go home straight away after, unless they are experiencing dizziness, in which case they may remain in the waiting room until they are feeling better.

The sample is labelled and sent to the laboratory for testing, which may involve looking at it under a microscope, or testing its reaction to certain chemicals, depending on what is being tested.

The results of some blood samples are available more quickly than others, but the dermatologist will advise how quickly you can expect to have the results – usually within 1-2 weeks at most.

If you have underlying medical conditions, or are regularly taking medications, it is essential that you let your dermatologist know when they take your medical history during consultation, since they might mean you are more susceptible to bleeding, dizziness or bruising.

Some people may experience more dizziness than others, and it may be beneficial to rest in the waiting room or have a cup of tea following your blood test until this regulates.

You may have more or less bruising afterward than other people who’ve had a blood test – this is usually dependant on how your skin typically bruises, but this may also be influenced by underlying health conditions or medications, which the dermatologist will advise you about beforehand.

There may be slight bruising and tenderness in the days after a blood test, and some people are prone to more visible bruising than others, but they should fade within 5-7 days.

Blood test results can usually be obtained over the phone, but you may need to attend further appointments, or regular follow-up appointments with the dermatologist for the treatment of your skin condition.